1. Preheat oven to 350°F (176°C). Prepare a 9 inch springform pan with a circle of parchment paper in the bottom and grease the sides.
2. To make the cake batter, beat the sugar and butter together until light in color and fluffy, 3-4 minutes. Don’t skimp on the creaming.
3. Add the sour cream and vanilla extract and mix until well incorporated.
4. Add the egg whites and mix until well combined.
5. Combine flour and baking powder in a separate bowl, then add half of the dry ingredients to batter and mix until well incorporated.
6. Add the milk and water and mix until well incorporated.
7. Add the remaining dry ingredients and mix until well incorporated and smooth.
8. Spread the cake batter evenly into the bottom of the prepared pan.
9. Bake for 18-20 minutes, or until a toothpick inserted comes out with a few crumbs. Set the cake aside to cool.

TO MAKE THE CHEESECAKE FILLING:

10. While the cake is cooling, make the cheesecake filling. Add the chocolate chips to a medium sized bowl.
11. Heat the heavy whipping cream until it begins to boil, then pour it over the chocolate chips and add the vanilla extract. Allow the mixture to sit for 3-4 minutes, then whisk until smooth. Set aside.
12. Add the cream cheese, sugar and flour to a large mixer bowl and beat on low speed until completely combined and smooth. Be sure to use low speed to reduce the amount of air added to the batter, which can cause cracks. Scrape down the sides of the bowl.
13. Add the sour cream and vanilla extract mix on low speed until well combined.
14. Add the eggs one at a time, mixing slowly to combine after each addition. Scrape down the sides of the bowl as needed to make sure everything is well combined.
15. When the cake layer has cooled, reduce the oven temperature to 300°F (148°C). Remove the sides of the springform pan and clean it off, the respray it with non-stick spray. You want to be sure it’s well done so that they cheesecake doesn’t stick to the sides after baking.
16. Reset the springform pan edges around the cake, then pour the chocolate mixture on top of the cake. Spread it into a fairly even layer, keeping it about a half inch or so away from the edge of the cake so that it stays in the center.
17. Add the cream cheese filling to the pan, beginning with the edges where the gap between the chocolate and the edge of the pan is, then fill in the center. The pan will be fairly full.
18. Prepare the pan for a water bath (see my method for preventing your water bath from leaking here) by wrapping the outside of the pan with aluminum foil, then place the springform pan inside another larger pan. Fill the outside pan with enough warm water to go about halfway up the sides of the springform pan. The water should not go above the top edge of the aluminum foil on the springform pan.
19. Bake for 1 hour 15 minutes. The center should be set, but still jiggly.
20. Turn off the oven and leave the door closed for 30 minutes. The cheesecake will continue to cook, but slowly begin to cool as well.
21. Crack the door of the oven for 30 minutes to allow the cheesecake to continue to cool slowly. This process helps prevent cracking.
22. Remove the cheesecake from the oven and water bath wrapping and refrigerate until firm, 5-6 hours or overnight. Once completely cool and firm, remove from the springform pan.

TO MAKE THE TOPPINGS:

23. While the cheesecake cools, make the toppings. To make the chocolate ganache, add the chocolate chips to a medium sized bowl.
24. Heat the heavy whipping cream until it begins to boil, then pour it over the chocolate chips and add the corn syrup and vanilla extract. Allow the mixture to sit for 3-4 minutes, then whisk until smooth. Set in the fridge to cool completely.
25. To make the pastry cream, put the egg yolks in a medium sized bowl and gently beat them together. Set aside.
26. Add the sugar, cornstarch and milk to a large saucepan and mix until smooth.
27. Cook, stirring continuously, over medium-high heat until mixture begins to thicken and bubble.
28. Reduce heat to medium and simmer for 2 minutes. Remove from heat.
29. Add a little bit of milk mixture to the egg yolks and whisk together, then add egg mixture to milk mixture. This process ensures that you don’t cook the egg yolks.
30. Place the pan back on the heat and bring to a light boil. Allow to boil for 2 minutes, stirring continuously.
31. Remove from heat and add butter and vanilla extract. Stir until smooth, then cover and set in the fridge to cool completely.

TO PUT IT ALL TOGETHER:

32. Remove the chocolate ganache from the fridge and put it into a piping bag fitted with your preferred piping tip. I used Ateco tip 849. If it seems a little firm, microwave for 5-10 seconds, just until it’s soft enough to use for piping.
33. Pipe the ganache around the edge of the cheesecake.
34. Add the pastry cream to the center of the cheesecake and spread evenly.
35. Cover the cheesecake and refrigerate until ready to serve. Cheesecake is best for 2-3 days.